Winter Outlook 2024-2025

[40/70 Benchmark]

I'll go through it all in great detail later this spring, but a bit of regression here in terms of my snowfall forecast....I have had some decent forecasts overall, namely 2022-2023, just not work out in terms of snowfall...but this year largely worked out, despite a pretty flawed forecast. I'm glad I was too warm, as opposed to cold because there was a definite bias in my forecasts.

I do not anticipate much more activity.

[40/70 Benchmark]

 

February Review & March 2025 Preview

Nature of Polar Vortex Split a Large Wrinkle for February Forecast

February Review

Here is the narrative forecast for February that was issued in November.

 

February Analogs: 2011, 2008, 2000, 1999,1972

The polar vortex should begin the month very strong, but watch for a potential SSW from about mid month onward.

The pace of moderate storms should increase for the first time all season, just as the warmer weather returns in February, however, a notable difference from many recent months of February is that it should not be prohibitively warm so as to entirely preclude some appreciable snowfall across the majority of the region. The month should finish 1 to 3F above average with near normal to perhaps just below normal snowfall. Northern New England should see above normal snowfall as the cold air source lurks close by in southeastern Canada, which will produce several front-end snowfall for much of southern New England and perhaps even into the northern mid Atlantic at times.

"SWFE"....AKA "Southwest Flow Events-

The primary source of deviation from the forecast this month was that a split of the polar vortex (PV) did indeed occur mid month, which represented the beginning of the window identified in the Eastern Mass Weather winter outlook.

 

 

However, this disruption of the PV initiated in the troposphere and then worked upwards. This obviously allowed the impact in terms of a severely negative AO to be realized immediately, whereas the forecast presumed the impetus for the disruption to be a sudden stratospheric warming (SSW), which would then take approximately 2-4 weeks to propagate down into the troposphere. 

 

 

Obviously the mean AO value ended up much lower for February than it would have had the PV disruption been triggered by stratospheric warming that would have taken until at least the end of the month to affect the lower levels.

It's clear in the 500mb plot how this altered the regime during the month of February across the continent relative to the forecast.

 

 

This faster than anticipated development of the AO blocking spilled over into the EPO domain in Alaska and combined with an unexpected +PNA to dump very cold air into the nation's mid section.

The strongly positive PNA this month will challenge the analog season of February 2000 as the most positive on record for a La Niña and is likely to end up the strongest La Niña seasonal +PNA on record.

 

 

This is likely to have longer term ramifications beyond the scope of this writing, but the implication for the month of February 2025 was a break in a longer term extratropical Pacific trend that combined with a polar vortex disruption that was triggered in the lower levels to produce a colder than forecast outcome.

 

 

 

The departure from the forecast is not as drastic locally as it was nationally, likely due in part to the well forecast +NAO allowing the cold to focus west of the region, as it often has over the course of the last several years. 

 

 

The +1-3 degree F regional forecast anomaly is likely to range instead from near normal to  -2 degrees F. Given that precipitation amounts are likely to finish near average, as expected, this has resulted in slightly above average snowfall instead of normal to slightly below average. 

 

 

 

 

However, the predominately positive NAO this month has indeed resulted in several mixed precipitation events, or southwest flow events, as expected. The positive nature of the NAO also likely played a role in the lobe of the PV post split initially drifting westward, which allowed one of the larger storms to phase of the west. The primary question left before entering is spring is whether or not a larger polar vortex disruption is triggered by a warming of the stratosphere, as implied by research conducted last fall pertaining to westerly QBO/solar max season.

March 2025 Preview

The focus of the March forecast last fall was whether or not there would be a Sudden Stratospheric Warming (SSW) that would induce a major disruption of the PV.

 

March Analogs: 2023x2, 2022, 2021, 2017 2014, 2001,1972

The polar vortex should weaken once again to an extent to close out the season, though confidence is not high in a major episode of blocking. The window for a SSW is through about the 20th of the month, so the impact on winter would largely depend on just how early it can take place. During February or at least the first week of March for maximum impact throughout southern New England. There is another window for a potential KU from approximately March 5 through the 19th, but confidence is low. The cold source should be relatively close by at the very least, not unlike February should major blocking not materialize. Near average to 2F above in the mean with near average precipitation inland and slightly below near the coast.  

 

The following is an excerpt from research cited pertaining to the increased likelihood for late season SSWs during westerly QBO seasons that occur near solar max.

 

 

 

 

 

These relationships between solar behavior and the NAO are evident in the graph above, with reds, denoting +NAO, very evident in the declining phase of the last several solar cycles. And Blue, indicative of -NAO, prevalent in the ascending portion of the cycles. What can also be deduced from the graphic above is that while solar max seasons are not as favorable as the ascending phase of the cycle for incidences of high latitude blocking, nor are they as hostile as the descending seasons. Thus winter seasons such as 2024-2025, which are near solar max, are not entirely devoid of blocking, however, nor is this season as prone to an intense round of late season blocking the magnitude of March 2023 given that the solar cycle was still ascending at that point. Be that as it may, solar max seasons are not entirely hostile to incidences of a disturbed polar vortex and this is evident when considering the best solar analogs of 1970 and 1999.

 

There was a split of the polar vortex on January 17, 1971, a displacement on March 20, 1971 and a displacement on March 20, 2000. While there was an easterly QBO evident during the 1970-1971 winter, the polar vortex displacement that took place in March of 2000 occurred during a westerly QBO, as will be the case this season. Thus the latter displacement seems worthy of more consideration for the coming season. When considering the three primary QBO analogs of 2016, 2020 and 2022 within a solar context, although none took place during solar max, 2022 was the closest, followed by 2016 and 2020, the latter of which is a poor solar match having taken place near solar minimum.

 

Given that the QBO analog of 2020-2021 took place near solar minimum, the early January 2021 SSW  is of least relevance as a viable analog occurrence this season. However, the February 2023 SSW, which is a better solar analog, lends more support to a later season potential polar vortex disruption along the lines of March 1971 and 2000. This notion is supported by research on high solar, westerly QBO seasons, which lends credence to the late winter/early spring displacement scenario.

 

 

 

 

The research clearly implies that a displacement of the PV triggered by a SSW beyond mid month is a distinct possibility based on the history of westerly QBO seasons that have occurred near solar max. There is some recent guidance that has aggressively indicated that a SSW would occur earlier than this, and yet other guidance suggests that 

 

 

 

 

While other guidance is more subdued and implies marginal conditions late in the month, which would like be of little consequence.

 

 

 

 

 

Regardless, any late SSW is unlikely to have a major impact on the nation in terms of notable winter weather during March, rather it would likely have implications for the weather pattern during the spring season. 

 

Here is a comparison of the March forecast composite from this past fall (left) with the latest CFS guidance composite (right).

 

 

And a similar temperature anomaly juxtaposition.

 

 

 

The risk to the forecast is likely a slighly warmer outcome and reduced likeliehood of a KU caliber winter storm owed to the expedited manifestation of last month's PV split impacting the February patternas , opposed to early March.

What is likely to be the final winter storm threat of the season for the region looks to take place in the vicinity of March 9. This signal is supported by teleconnector convergence in both the Pacific.

 

 

And the Atlantic side.

 

 

Bolstering confidence in the threat period is cross ensemble support.

 

 

The primary mitigating factor at this time would appear to be the positioning of the PNA ridge slightly too far to the east, which would perhaps favor an out to sea track and/or later development.

 

Thereafter the early indications are that the MJO may approach phase 3 and then the Maritime continent, which would effectively end winter 2024-2025 with a deep RNA derived warm burst.

 

 

 

 

 

[40/70 Benchmark]

 

Winter Coming to a Close Despite Expected Late Stratospheric Warming

Final Stratospheric Warming Too Late for Much Fanfare as Per Analogs

Analog Data of Great Utility

The EasternMassWeather March preview cited last fall's research of solar max/westerly QBO seasons as support for an early spring Sudden Stratospheric Warming (SSW) event that would occur too late to have major ramifications in terms of winter weather for the forecast area. The March 20, 2000 SSW and resultant displacement of the polar vortex was listed as a primary analog last fall and guidance has continued hone in on a very similar stratospheric evolution throughout the first half of the month of March. 

 

 

 

Accordingly, the resultant weather pattern over the arctic if forecast to respond in a similarly like manner to latter March 2000.

Late March Blocking Likely to Interrupt Pleasant Spring Onset

The weather pattern next week looks seasonably mild and relatively pleasant, as the early seeds of change are planted in the arctic stratosphere.

 

 

The evolution over the arctic stratosphere will begin to manifest itself into the 500mb pattern during the final week of the month, as the development of a negative AO and NAO will be signify the development of high latitude blocking in response to the ongoing stratospheric warming.

 

 

The similarity to the latter March 2000 blocking pattern to the long range modeled evolution is apparent.

 

 

However, the north Pacific pattern looks slightly more conductive to potentially wintry weather over the northern New England ski resorts, and some nuisance or trace amounts of snowfall over southern New England cannot be ruled out. Be that as it may, as has been the case throughout the winter season, the cold appears merely seasonable in severity, which is unlikely to be supportive of significant early spring snowfall across the forecast area by the end of the month and into early April.

 

[40/70 Benchmark]

 

 

March Slightly Warmer Than Forecast

 West Pac Changes Lead to Warmer Outcome Despite PV Disruption

The major assault on the polar vortex that begin just prior to the midway point of the month was very well forecast by Eastern Mass Weather.

The following is an excerpt from research cited pertaining to the increased likelihood for late season SSWs during westerly QBO seasons that occur near solar max.

 

 

 

 

 

These relationships between solar behavior and the NAO are evident in the graph above, with reds, denoting +NAO, very evident in the declining phase of the last several solar cycles. And Blue, indicative of -NAO, prevalent in the ascending portion of the cycles. What can also be deduced from the graphic above is that while solar max seasons are not as favorable as the ascending phase of the cycle for incidences of high latitude blocking, nor are they as hostile as the descending seasons. Thus winter seasons such as 2024-2025, which are near solar max, are not entirely devoid of blocking, however, nor is this season as prone to an intense round of late season blocking the magnitude of March 2023 given that the solar cycle was still ascending at that point. Be that as it may, solar max seasons are not entirely hostile to incidences of a disturbed polar vortex and this is evident when considering the best solar analogs of 1970 and 1999.

 

There was a split of the polar vortex on January 17, 1971, a displacement on March 20, 1971 and a displacement on March 20, 2000. While there was an easterly QBO evident during the 1970-1971 winter, the polar vortex displacement (PV) that took place in March of 2000 occurred during a westerly QBO, as will be the case this season. Thus the latter displacement seems worthy of more consideration for the coming season. When considering the three primary QBO analogs of 2016, 2020 and 2022 within a solar context, although none took place during solar max, 2022 was the closest, followed by 2016 and 2020, the latter of which is a poor solar match having taken place near solar minimum.

 

Given that the QBO analog of 2020-2021 took place near solar minimum, the early January 2021 SSW  is of least relevance as a viable analog occurrence this season. However, the February 2023 SSW, which is a better solar analog, lends more support to a later season potential polar vortex disruption along the lines of March 1971 and 2000. This notion is supported by research on high solar, westerly QBO seasons, which lends credence to the late winter/early spring displacement scenario.

 

 

 

 

The research clearly implies that a displacement of the PV triggered by a SSW beyond mid month is a distinct possibility based on the history of westerly QBO seasons that have occurred near solar max, and this is precisely what took place. Note the displacement of the PV in concert with the warming polar stratosphere that had already begun prior to mid month.

 

The event continued to evolve until a reversal of the zonal winds occurred around March 20th, as suggested by the analogs.

 

 

The research also suggested that any cold resulting from the PV disruption would be insufficient and/or too late to bias the monthly mean negative and that has also proven correct.

 

Warmer & Drier Than Average March With Very Little Snowfall

Eastern Mass Weather forecast anywhere from near normal top +2F positive mean monthly departures for the region, but this is likely to verify anywhere within a range of approximately +3 to +5F due in large part to the reversal of the prominent -WPO pattern this season.

 

 

 

The lower heights in the vicinity of Northeastern Siberia in the +WPO composite are very apparent.
 

 

This is consistent with the 500mb pattern throughout most of the month.

 

 

As well as the aforementioned analog season of 2000, which perhaps should have been weighted more heavily throughout the pattern half of the season.

 

 

 

It is fair to consider whether or not the behavior of the polar stratosphere had any impact on the evolution of the Pacific given the uncanny similarities. 

The drier than average pattern, especially near the coast, was well forecast and undoubtedly played a role in with southern New England saw very little snowfall throughout the month.

 

 

March Conclusions

The forecast for the month of March was not bad overall, however, its success was limited by an incorrect assessment of the WPO in conjunction with an underestimation of just how unfavorable the polar domain would be despite the major polar vortex disruption.

 

The PNA was not a prevalent factor for the majority of March, but its decided descent into strongly negative territory to close the month may assist in mitigating any potential impacts of the ongoing stratospheric warming for the region.

 

 

 

 

[40/70 Benchmark]

On 11/15/2024 at 11:22 AM, 40/70 Benchmark said:

Just realized I never threaded this in the NE subforum, which I usually do....I prefer to update in here, rather than the main forum.

 

https://easternmassweather.blogspot.com/2024/11/using-past-forecasting-difficulty-to.html

 

 

 

 

 

 

I'll go over the post-mortem in depth about a month from now, but looks like the snowfall worked out for the most part. The overall forecast def. had issues, though.

[40/70 Benchmark]

Looks like Worcester may have been my largest miss...followed by Concord, NH.

[40/70 Benchmark]

Just eye-balling, I think I landed in my range on 8/15 locales, which would be a new high-water mark....and desperately needed after the past couple of horror-shows. There is obviously luck involved with snowfall because its subject to so much variance...I don't think some of the "poor" forecasts were as bad as the snowfall made them appear, and this seasons's forecast wasn't as good as the snowfall made it appear...kind of like 2014-2015 in that a flawed forecast got "lucky" in that the snowfall was right for the wrong reason. It evens out in the end.